1. Field of the Disclosure
The disclosure refers to a leakage search assembly having a sniffing probe, which comprises a main device containing a vacuum pump and a tracer gas sensor and which is connected with a sniffing probe via a flexible tubing.
2. Discussion of the Background Art
DE 44 45 829 A1 (Leybold AG) describes a counter-flow sniffing leakage search device having a high vacuum pump stage at the end of a sniffing hose. A sniffing hose of approximately 4 m in length is used which is designed as a capillary line and has an inner diameter of approximately 0.4 mm. The sniffing hose provides a throttling effect required to maintain the vacuum generated at its outlet end.
DE-OS 24 41 124 describes a leakage search device having a sniffing hose, wherein the hose has a relatively large diameter. A throttle is provided right in front of the tracer gas sensor, which is a mass spectrometer. By arranging the throttle right in front of the tracer gas sensor, the vacuum pump can convey the gas to be analyzed more quickly from the inlet of the sniffing probe to directly in front of the throttle, i.e. to the tracer gas sensor. Thus, the response time that depends on the length of the flexible tubing, is reduced.
German patent application DE 10 2005 009 713 (not pre-published) describes a leakage search assembly having a sniffing probe, where the flexible tubing connecting the sniffing probe to a main device includes at least two capillary lines which may be selectively closed either in the main device or in the sniffing probe. By opening of one or several valves selectively, it is possible to select the capillary line through which air is to be aspirated. Thus, by choosing a capillary line with a specific cross section, the dead time can be varied. Moreover, two different types of devices that operate with different gas flow rates can be used in combination with the same flexible tubing.
It is a problem of sniffing leakage search that large portions of the item under test have to be searched as quickly as possible to first find a leak in that process. Thereafter, the leak found has to be assessed with respect to its size, the reference value used being a previously set trigger signal. These two requirements are in conflict with each other, since                a short response time and a good distance sensitivity are required for an efficient leakage search, and        for a quantitative evaluation, however, a high stability of the signal is needed that can not easily be achieved in a quick measurement.        
Leakage search assemblies are known from practice that allow a leakage search mode and a leakage rate measuring mode to be performed. With assemblies having a differentiating display, where the derivative of a measurement signal is determined as a function of time so as to suppress constant background concentrations, the highest possible pre-amplifier sensitivity is selected in the search mode so as to detect low concentrations of leakage gas already at a greater distance from the leak. With assemblies having a non-differentiating direct display, a search trigger level is defined that is significantly lower than the actual trigger limit. In either instance, increasing the sensitivity or lowering the trigger level does not enhance the distance sensitivity, because the cloud of leakage gas forming around the leak is very limited, especially with heavy gases having a low coefficient of diffusion, such as refrigerants, for example. Should the amplification be increased, a greater signal noise would have to be accepted. If the noise is reduced by a longer averaging time, the signal will rise much more slowly, decreasing the possible searching speed. With non-differentiating displays, slow background variations can only be corrected by repeated manual zero point adjustment which is difficult given the increased sensitivity in the search mode.
It is the object of the disclosure to provide a leakage search assembly having a sniffing probe, which allows to search large portions of an item under test as fast as possible and to quickly find each leak in the process, and which also allows for an exact determination of the size of the leak.